1. Field of the Invention
This invention relates to an image pickup apparatus and a lens position adjustment apparatus, and more particularly to an image pickup apparatus and a lens position adjustment method wherein adjustment of the lens position or driving of the lens is performed, for example, for focusing control.
2. Description of the Related Art
An image pickup apparatus such as a still camera or a video camera incorporates an automatic focusing mechanism for automatically focusing on an image pickup subject. As one of common methods for focusing control, a method of discriminating the degree of the contrast of pickup image data acquired through a lens is available. According to the method just mentioned, a particular region of a picked up image is set as a signal acquisition region (spatial frequency extraction area) for focusing control. Then, it is decided that, as the particular region indicates a higher contrast, the image pickup data is nearer to an in-focus state, and where the contrast is low, the image pickup data is far from an in-focus state. Then, the lens is driven so as to raise the contrast to adjust the focus.
As a contrast decision processing method, a method is applied wherein high frequency components in a particular region are extracted and integration data of the extracted high frequency components is produced and then the level of the contrast is decided based on the produced high frequency component integration data. In particular, a high frequency component integration value is calculated for the decision of the level of the contrast and used as an evaluation value. A focusing lens is driven so as to maximize the evaluation value thereby to achieve automatic focusing. It is to be noted that focusing and a driving method for a lens are disclosed, for example, in Japanese Patent Laid-Open No. Hei 4-000421.
In order to carry out automatic focusing, it is necessary to drive the lens using an evaluation value described above as a pointer. The lens driving mechanism is formed typically from a voice coil motor. However, a lens driving mechanism including a voice coil motor or the like generally has a hysteresis. Therefore, if the control voltage value determined based on the evaluation value is applied to the voice coil motor to perform lens driving control, then this gives rise to a problem that the lens position differs depending upon whether the application voltage is set to a target voltage value (V1) from a minimum value (MIN) or is set to the target voltage value (V1) from a maximum value (MAX).
In order to solve the problem just described, for example, the following process is performed. In particular, if a target voltage value (V1) is determined, then the application voltage to a lens driving mechanism including a voice coil motor or the like is set once to the minimum value (MIN) so that the lens is positioned at an end of a driving range therefor, and then the application voltage is raised from the minimum value (MIN) to the target voltage value (V1) so that the lens is finally set to the target lens position.
However, where such lens position control as just described is carried out, much time is required for the adjustment of the position of the lens, and this gives rise to a problem that long time is required for automatic focusing. On the other hand, where such control is not carried out, there is a problem that displacement of the lens set position based on the hysteresis appears.